2 Answers
2

Some store the data on the SD car in a public folder and as long as you don't manually delete the folder after you uninstall the app, it will still be there when you reinstall.

Other apps store data this way but have their configuration data in the secured portion of the internal memory and that data is lost when you uninstall (example: podcast app that stores the podcasts, and they subscription data on the SD card but the login, password and settings data internally. You'll still have your podcasts and subscriptions but you'll have to re-enter the other data).

Some apps store all their data in the protected memory so you'll lose everything when you uninstall unless you use some kind of backup utility.

Angry birds stores data in the protected portion of the internal memory and all is lost when you uninstall. There are apps that specifically backup Angry Birds data and other apps that backup apps. There are so many there's no point in mentioning them here but just search the market for "Angry Birds Backup" or "App backup".

Titanium Backup is the best in my opinion but you need to be rooted to use it, while others you do not.

Use a program like Titanium Backup to back up the data, then remove the program and install the new one, then restore the data. But. Often the data will be incompatible between versions and this may lead to force closes.